The CVs I receive from young people who’ve attended comprehensives are invariably so badly punctuated that they go straight in the bin. One grammar school-educated friend, a barrister, would dearly love to give the annual pupillage at his chambers to someone from a state school. But when they so often lack the poise, confidence and oratory skills of their public school peers, that just isn’t possible.

The Class structure in the United Kingdom, is hereditary. A pupil will often attend a Public School, that was attended by his father, and grandfather.
The state pupil is at a disadvantage before he enters a comprehensive school. He will adopt the culture and language of his parents. If his father is a Billingsgate porter, well, enough said.

Oh, FFS. I've met enough people of old money to know that many are vicious sharks interested only in self-advancement and over dead bodies at that, manners being a veneer at best. And as for Billingsgate's porters, many a fine gentlemen and lady, well read, intellectual and refined, are to be found among them. As to what this has to do with grammar schools vs. comprehensives, who knows?

Talk about this, and especially the language people from different (class and educational) backgrounds habitually use, always makes me think of the theory of 'elaborated and restricted codes' (in language use) devised by the sociologist Basil Bernstein. See e.g. here for an explanation.

Interestingly, chess players analysing a chess game, or indeed talking about chess in general a lot of the time, offer a good example of 'restricted code' in action.